Cleaning moving webs by passage between opposed flexible polyurethane foam wipers

ABSTRACT

In the production of thin polymer films of up to about 6 microns thickness by casting a solution of the polymer on to a moving support web, the carrier web is cleaned prior to coating by passing it at a speed of at least 15 ft./min. between at least one pair of dry wipers formed of a non-dusting, non-linting, resilient material, such as flexible polyurethane foam.

ite'd States BETWEEN OPPOSEQ FLEXIBLE POLYURETHANE FOAM WIPERS Inventor: John Norman Cheetham, Ashtead,

England I Assignee: Yarsley Research Laboratories Limited, Chessington, Surrey, England Filed: May 8, 1973 Appl. N0.: 358,392

Foreign Application Priority Data 11 1 111 3,852,109 Clieetharn 1 Dec. 3, 1974 1 CLEANING MOVING WEBS BY PASSAGE [56] References Cited UNITED sTATEs PATENTs 3,245,835 4/1966 1 Gallino 15/l.5 X

FOREIGN PATENTS OR APPLICATIONS 47,998 6/1930 Norway 15/l.5

Primary Examiner-S. Leon Bashore Assistant ExaminerRichard H. Tushin Attorney, Agent, or Firm-Bacon & Thomas 5 7] ABSTRACT In the production of thin polymer films of up to about 6 microns thickness by casting a solution of the polymer on to a moving support web, the carrier web is cleaned prior to coating by passing it at a speed of at least 15 ft./min. between at least one pair of dry wipers formed of a non-dusting, non-linting, resilient material, such as flexible polyurethane foam.

12 Claims, 3 Drawing'Figur'es CLEANING MOVING WElBS BY PASSAGE BETWEEN OPPOSED FLEXIBLE POLYURETHANE FOAM WIPERS This invention is concerned with the production of thin polymer films.

It is known to make thin films of from 0.5 to 6 microns thickness of various polymers, such as cellulose esters, cellulose ethers, polystyrene, polyurethane, polysulphones, and polycarbonates, by casting a solution of the polymer on to a moving support web and drying the coating obtained to remove the solvent and leave a thin film of the polymer on the support web, and subsequently stripping the thin film from the support web. The thin films thus obtained are used for the production of capacitors after they have been metallised on one surface.

It is essential that the support web should be absolutely clean and free of dust and other particulate contaminants before the polymer solution is cast on to it in order toavoid the formation of pinholes and other defects in the thin film.

Hitherto it has been thought necessary to cleanthe support web, prior to'passing it to the casting station, by passing it through a solvent bath containing one or more pairs of immersed wipers between which the support web is passed. The use of a solvent bath necessitates passing the support web through a drying station before it is passed to the casting station and desirably also requires a solvent recovery system associated with.

the drying station.

We have now found, unexpectedly, that an acceptably clean and dust-free support web can be obtained by simply passing the support web between one or more pairs of dry wipers at a rate of at least feet/minute and, preferably, at least feet/minute. The wipers should, of course, extend across the width of the support web and should be formed of a non-dusting, non-linting resilient material.

According to the present invention, therefore, we provide a method of cleaning a continuous support web prior to forming a thin polymer film thereon, which comprises passing the support web between at least one pair of dry wipers, one wiper of the pair bearing against one surface of the support web and the other wiper bearing against the other surface and the wipers being formed of a non-dusting, non-linting resilient material, at a rate of at least 15 feet/minute.

The present invention also comprises apparatus for cleaning a continuous support web prior to the formation of a thin polymer film thereon, which comprises at least one pair of dry wipers formed of a non-dusting, non-linting resilient material, and means for passing the support web between the wipers so that one wiper of the pair bears against one surface of the support web and the other wiper bears against the other surface;

. A preferred material for the wipers is flexible polyurethane foam having a nominal density of 2 lbs./cu.ft.

In order that the invention may be more fully understood, a preferred embodiment of cleaning apparatus, and theoperation thereof, will now be described, by

way of example, with reference to the accompanying FIG. 3 is a diagrammatic elevation of a cleaning apparatus comprising four wiper assemblies as shown in FIG. 1.

Referring to FIGS. 1 and 2, the wiper assembly comprises an open metal frame 10, the length of which is somewhat greater than the width of the support web to be treated, and two L-shaped clamping plates 11 and 12, which are adjustably secured to two of the long edges of the frame 10 by screws 13 passing through slots 14 in the plates 11 and 12. Flexible polyurethane wiper strips 15 and 16 are held in position by compression of one long edge of the wipers between the frame 10 and the plates 11 and 12 respectively.

In operation, the support web 17 is passed between the wipers 15 and 16 so that one wiper bears against one surface of the web and the other wiper against the other surface, the portions of the wipers adjacent their free edges forming an acute angle of approximately 30 with the support web, the direction of travel of which is indicated by the arrows in FIG. 2.

In a particular embodiment for treating a 6 inch wide support web the wipers l5 and 16 were formed of onefourth inch thick flexible polyurethane foam having a nominal density of 2 lbs./cu.ft., each wiper being 7 inches long and 1% inches wide. i

. It is preferred to provide four wiper assemblies of the kind shown in FIGS. 1 and 2, a suitable arrangement of these assemblies being shown in FIG. 3. As seen from this Figure, the support web 17 is passed over an idler roll 18, under an idler roll 19, then successively through two wiper assemblies 20 and 21 arranged in series, around in idler roll 22, through two further wiper assemblies 23 and 24 arranged in series, and then around an idler roll 25 and from'the latter is passed on to the coating station where the thin polymer film is formed thereon. The wiper assemblies 20, 21, 23 and 24 are as shown in FIGS. 1 and 2.

In some cases it has been found advantageous to earth the metal frames 10 of the wiper assemblies, suitably to the main machine framework, in order to prevent excessive build-up of the static charges when the support web passes between the polyurethane wipers.

As indicated above, the rate of travel of the support web should be at least 15 feet/minute and, preferably, at least 20 feet/minute; an arrangement as shown in FIG. 3 has been successfully operated with a 6 inch wide carrier web at web speeds of up to feet/minute and higher speeds can be used if desired. However it has been found that if the support web speed is less than 15 feet/minute,the cleaning effect of the dry wipers is inadequate and the thin film produced will be found to contain defects.

What is claimed is:

1. A method of cleaning a'continuous support web prior to forming a thin polymer film thereon, which comprises the step of passing the support web at a rate of at least 15 feet/minute between at least one pair of dry wipers, one wiper of the pair bearing against one surface of the support web and the other wiper bearing against the other surface and the wipers being formed of a flexible polyurethane foam material.

2. The method set forth in claim 1, wherein Sadi support web is passed at a rate of at least 20 feet/minute.

3. The method set forth in claim 1 wherein said flexible polyurethane foam material has a nominal density of 2 pounds/cubic foot.

4. The method set forth in claim 1, wherein each said wiper is in the form of a strip, a free edge of which bears against said support web, and the portion of each said wiper adjacent said support web makes an acute angle with said support web pointing in the direction of travel of said support web.

5. The method set forth in claim 4, wherein said angle is about 30.

6. The method set forth in claim 1, wherein said support web is passed between four pairs of said wipers.

7. Apparatus for cleaning a continuous support web prior to the formation of a thin polymer film thereon, which comprises at least one pair of dry wipers formed of a non-dusting, non-linting flexible polyurethane foam material, means supporting said wipers in opposed relation on opposite side of the path of a support web to be cleaned for engagement with said support web, and means for passing the support web between said wipers at a rate of at least feet/minute so that one wiper of the pair bears against one surface of said support web and the other wiper bears against the other surface.

8. Apparatus as set forth in claim 7 wherein said flexible polyurethane foam material has a nominal density of 2 pounds/cubic foot.

9. Apparatus as set forth in claim 7, wherein each said wiper is in the form of a strip which is clamped along one long edge and the opposite long edge is positioned to bear against said support web, the portion of said wiper adjacent its free edge forming an acute angle with said support web pointing in the direction of travel of said support web.

10. Apparatus as set forth in claim 9, wherein said angle is about 30.

11. Apparatus as set forth in claim 9, wherein each said pair of wipers is clamped in a metal frame which is grounded.

12. Apparatus as set forth in claim 7, comprising four pairs of wipers. 

1. A METHOD OF CLEANING A CONTINUOUS SUPPORT WEB PRIOR TO FORMING A THIN POLYMER FILM THEREON, WHICH COMPRISES THE STEP OF PASSING THE SUPPORT WEB AT A RATE OF AT LEAST 15 FEET/MINUTE BETWEEN AT LEAST ONE PAIR OF DRY WIPERS, ONE WIPER OF THE PAIR BEARING AGAINST ONE SURFACE OF THE SUPPORT WEB AND THE OTHER WIPER BEARING AGAINST THE OTHER SURFACE AND THE WIPERS BEING FORMED OF A FLEXIBLE POLYURETHANE FOAM MATERIAL.
 2. The method set forth in claim 1, wherein sadi support web is passed at a rate of at least 20 feet/minute.
 3. The method set forth in claim 1 wherein said flexible polyurethane foam material has a nominal density of 2 pounds/cubic foot.
 4. The method set forth in claim 1, wherein each said wiper is in the form of a strip, a free edge of which bears against said support web, and the portion of each said wiper adjacent said support web makes an acute angle with said support web pointing in the direction of travel of said support web.
 5. The method set forth in claim 4, wherein said angle is about 30*.
 6. The method set forth in claim 1, wherein said support web is passed between four pairs of said wipers.
 7. Apparatus for cleaning a continuous support web prior to the formation of a thin polymer film thereon, which comprises at least one pair of dry wipers formed of a non-dusting, non-linting flexible polyurethane foam material, means supporting said wipers in opposed relation on opposite side of the path of a support web to be cleaned for engagement with said support web, and means for passing the support web between said wipers at a rate of at least 15 feet/minute so that one wiper of the pair bears against one surface of said support web and the other wiper bears against the other surface.
 8. Apparatus as set forth in claim 7 wherein said flexible polyurethane foam material has a nominal density of 2 pounds/cubic foot.
 9. Apparatus as set forth in claim 7, wherein each said wiper is in the form of a strip which is clamped along one long edge and the opposite long edge is positioned to bear against said support web, the portion of said wiper adjacent its free edge forming an acute angle with said support web pointing in the direction of travel of said support web.
 10. Apparatus as set forth in claim 9, wherein said angle is about 30*.
 11. Apparatus as set forth in claim 9, wherein each said pair of wipers is clamped in a metal frame which is grounded.
 12. Apparatus as set forth in claim 7, comprising four pairs of wipers. 